Stats not updating

Have installed ISPconfig3 and UBuntu 11.04. Have 6 web domains. Setup stats via the gui interface using Awstats for all the websites. Now only 1 site will produce stats and it has only done it for one night, the other sites when I try to access the stats I receive a ERROR 500 Internal Server Error. Check the error logs for the site and this is what it shows:

(2)No such file or directory: Could not open password file: /var/www/clients/client5/web3/.htpasswd_stats